Pulmonary anthrax, a rare but extremely severe form of anthrax, is initiated by phagocytosis of Bacillus anthracis spores by alveolar macrophages (AMs). The current, Protective Antigen (PA) based, vaccine requires several boosts, is reactogenic and its efficacy, based on animal exposure studies, has been variable. Spore antigens, by themselves, as vaccine components enhance protection against experimental infection. As evident by the illicit dissemination of anthrax spores to the public in the fall, 2001, the intense efforts to identify new therapeutics and vaccines are warranted. A defined spore component could dramatically enhance the efficiency of a vaccine over the currently available product. Hypothesis: We draw upon prior studies to formulate the hypothesis to be tested: 1) specific antibodies to anthrax spore antigen(s) will confer passive protection and promote AM killing of opsonized spores; 2) vaccine preparations containing these antigens, in conjunction with PA, are likely to confer protective immunity to inhalation anthrax. Research Design and Methods; Aim 1: Produce monoclonal antibodies to B. anthracis spores. The studies will use Sterne strain (pXO 1+, pXO2-) B. anthracis spores to immunize mice and produce monoclonal antibodies. Anti-spore antibodies will be selected by using whole spore in an ELISA. Antibodies will be grouped according to antibody specificity and isotype. Aim 2: Select antibodies that can transfer passive protection in vivo and that promote killing by human and murine AMs in vitro. Anti-spore antibodies will be screened for their ability to promote spore killing by AMs as measured by colony forming units following phagocytosis. In parallel, anti-spore antibodies will be screened for their ability to confer passive protection against B. anthracis spore challenge in mice. Aim 3: The antibodies selected in Aim 2 will be used to isolate peptide mimetics from phage display libraries. Peptides will be tested for their ability, with appropriate carrier, to generate anti-spore antibodies. The validation of the isolated peptides and variants, in conjunction with PA, in virulent inhalation challenge studies will be part of an SBIR phase II proposal. Significance: This research is relevant to the potential to develop novel vaccine formulations and therapeutics to counter inhalation anthrax.